The background of the invention will be discussed in two parts.
1. Field of the Invention
This invention relates to shielding of electronic components, and more particularly, to a method and apparatus for electromagnetic interference (EMI) and radio frequency interference (RFI) shielding of components on a printed circuit board.
2. Description of the Prior Art
Shielding of electronic components for the suppression of EMI/RFI emission has been a method utilized virtually since the advent of electronic devices. Shielding of circuit components and electronic devices utilized in computers is commonplace, although with modern printed circuit board technology, the problem of shielding and the solution to shielding varies.
One approach to shielding has been to solder a half shield to the top surface of the printed circuit board, thus shielding only those components which require shielding. While this does not provide total shielding since the bottom surface of the printed circuit board to which the selected components are soldered is not enclosed, this approach has been adequate in some applications. With this method, the shield can be soldered to the printed circuit board at the same time the electronic components are soldered to the board, such as by wave soldering. The use of wave soldering as a means of affixing the shield to the board is inexpensive, but suffers some drawbacks. Since the components beneath the shield will be concealed, along with the surface area of the board thereunder, this method does not allow for cleaning, inspection and electrical test of the circuit board after wave soldering. As an alternative to allow for cleaning, inspection and test, the shield can be hand-soldered to the printed circuit board thereafter; however, this method is labor intensive and thus, expensive.
In certain critical applications, total shielding is mandated, that is the components require total shielding, above and below the printed circuit board. In such instances, shielding of the printed circuit board has been by the method of encapsulation of the entire board in a metal enclosure. Encapsulation of the entire circuit board is expensive, and in many applications, such encapsulation may not be possible or desirable due to size and weight constraints.
Therefore, in accordance with an aspect of the invention, it is a feature to provide a new and improved method and apparatus for shielding components on a selected portion of a printed circuit board.